Method for the production of thin film materials based on modified transition metal sulfides and their use in the production of fire warning sensors

Abstract

The application discloses a preparation method of a modified transition metal sulfide-based film material and application of the film material in preparation of a fire early warning sensor. The application adopts a ball milling / ultrasonic preparation process, utilizes a biomass molecule containing a hydroxyl group to realize modification of monolayer / oligolayer TMDs nanosheets and further batch preparation, and endows the TMDs nanosheets with good water dispersibility. In addition, due to weak force between the TMDs nanosheets, the network formed by the TMDs nanosheets generally has an ideal strength, and therefore, a one-dimensional cellulose nanofiber with a high aspect ratio is introduced to improve the flexibility and mechanical strength of the two-dimensional TMDs nanosheet network. On one hand, the cellulose nanofiber with a high aspect ratio has excellent mechanical properties. On the other hand, a large number of oxygen-containing functional groups existing on the surface of the modified TMDs nanosheet can form hydrogen bonds with the hydroxyl groups in the structure of the cellulose nanofiber, so that the mechanical strength of the composite film is further improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of functional materials, and particularly relates to a preparation method of a modified transition metal sulfide-based thin film material and application of the thin film material in preparation of a fire early warning sensor. BACKGROUND

[0002] The use of fire by human beings has accompanied the history of human civilization. However, once out of control, fire is easy to cause a fire disaster, which poses a serious threat to the safety of human life and property and the ecological environment. Especially in the modern social background, with the continuous development and application of various kinds of flammable polymer materials, the frequency of fire accidents caused thereby is also rising. At present, a fire early warning system plays a key role in early fire detection, provides valuable time for personnel evacuation, and greatly reduces the loss of life and property caused by fire. However, the traditional fire early warning sensor (such as an infrared sensor and a smoke sensor) has the shortcomings of long fire response time (> 100 s) and difficulty in realizing outdoor environment application. Therefore, it is particularly important to design and develop a new type of fire early warning material and system with a rapid fire detection function.

[0003] Mai et al. designed and developed a flame-retardant graphene oxide / silicone intelligent coating based on the mechanism of resistance transition caused by thermal reduction of graphene oxide at high temperature, and developed a new type of fire early warning system based on the coating (ACS Nano, 2018, 12, 416-424). Afterwards, the work of graphene oxide-based fire early warning film / coating was developed and reported. CN109021983A discloses a preparation method of a modified graphene oxide flame-retardant film and fire early warning application thereof. The patent utilizes the mechanism that ascorbic acid can promote the thermal reduction of graphene oxide to prepare a composite film material, which realizes the function of rapid alarm at low temperature (lower than 250℃). However, due to the irreversibility of the thermal reduction of graphene oxide, the composite film cannot realize multiple cycle alarms, and the material system cannot be applied to some complex environments where the fire may rekindle (such as forest fires). Therefore, CN111254737A discloses a multifunctional MXene coating, a preparation method thereof and application thereof in fire cycle detection and early warning. The technology takes MXene as the main body, combines water-soluble polymer PVP / PEG and fluorine-containing silane to prepare a multifunctional MXene coating which is hydrophobic, flame-retardant and can cycle fire detection. However, MXene has a high cost, the preparation process involves the use of a large amount of harmful reagents (hydrofluoric acid), and cannot be prepared in batches. Therefore, it is of important practical application value to design a low-cost intelligent material which can rapidly / cycle fire early warning. SUMMARY

[0004] The present application aims at the above-mentioned deficiencies in the prior art, and provides a preparation method of a modified transition metal sulfide-based thin film material and application thereof in preparation of a fire early warning sensor.

[0005] In the present application, unlike the graphene oxide-based sensor material which can only provide single early warning (irreversibility of thermal reduction), the transition metal sulfide (TMD) belongs to a semiconductor material, and the resistance of the material itself can change with the change of temperature and has reversibility. Therefore, as long as the material is changed from normal temperature to high temperature, the material can be changed from an insulating state to a conductive state, and after being connected to an early warning system, the cyclic early warning function of fire can be realized. In addition, due to the excellent thermal stability of TMDs, the material has good flame retardancy and structural stability under flame conditions, thereby ensuring the reliability of the fire early warning performance. However, the TMD raw material usually exists in the form of a multi-layer block, which is not conducive to the preparation of a composite thin film material and seriously affects the exertion of its own physical properties. In addition, due to the lack of active functional groups on the surface, the dispersibility of the TMD raw material in the solvent is poor, and it is easy to form sediment, which is not conducive to the compounding and processing of the material. Therefore, it is particularly important to realize the exfoliation and surface modification of the TMD sheet. Herein, a ball milling / ultrasonic preparation process is adopted, and biomass molecules containing hydroxyl groups are used to realize the modification and batch preparation of single-layer / oligolayer TMD nanosheets, and the TMD nanosheets are endowed with good water dispersibility. In addition, due to the weak interaction between the TMD nanosheets, the network formed thereby generally has an unsatisfactory strength, and therefore, higher aspect ratio cellulose nanofibers are introduced to improve the flexibility and mechanical strength of the two-dimensional TMD nanosheet network. On the one hand, the cellulose nanofiber with a higher aspect ratio has excellent mechanical properties. On the other hand, the hydroxyl groups in the structure can form hydrogen bonds with the large number of oxygen-containing functional groups on the surface of the modified TMD nanosheets, thereby further improving the mechanical strength of the composite thin film. The above techniques are the keys to preparing a low-cost, mechanically good, and fast / cyclic early warning TMD-based intelligent thin film material.

[0006] The present application provides a preparation method of a modified transition metal sulfide-based thin film material, which comprises the following steps:

[0007] Step 1: Biomass molecules containing hydroxyl groups are used as a modifier to modify and exfoliate the blocky TMDs through a ball milling process, and modified TMDs are obtained.

[0008] Step 2: The modified TMD powder obtained in step 1 is dispersed in deionized water, and the TMDs are further exfoliated under water bath ultrasonic conditions. After centrifugation and washing, a stable modified TMD nanosheet water dispersion is obtained.

[0009] Step 3: mixing the modified TMDs nanosheet aqueous dispersion and the cellulose nanofiber aqueous dispersion, and obtaining a uniform mixed solution after magnetic stirring.

[0010] Step 4: transferring the obtained mixed solution into a mold, and drying in a blast oven to obtain a composite film.

[0011] In step 1, the hydroxyl-containing biomass molecules are one or more of tannic acid, sodium alginate, and cellulose microcrystals.

[0012] In step 1, the TMDs are one or more of molybdenum disulfide, tungsten disulfide, molybdenum diselenide, and tungsten diselenide. The size of the bulk TMDs is in the range of 10-30 μm.

[0013] In step 1, the ball milling speed is 200-500 rpm, and the ball milling time is in the range of 2-6 h.

[0014] Further, the mass ratio of the hydroxyl-containing biomass molecules to the TMDs is 1:1 to 1:3.

[0015] In step 2, the ultrasonic power is in the range of 50-200 KW, the ultrasonic time is in the range of 10-60 min, the centrifugal speed is in the range of 3000-8000 rpm, the centrifugal time is in the range of 5-20 min, and the washing times are in the range of 1-5 times.

[0016] In step 2, the mass ratio of the modified TMDs powder to deionized water is in the range of 1:20 to 1:100.

[0017] In step 3, the cellulose nanofiber has a diameter in the range of 50-200 nm and a length in the range of 5-15 μm.

[0018] Further, the mass ratio of the cellulose nanofiber to the modified TMDs nanosheet is in the range of 1:1 to 1:2.

[0019] In step 3, the magnetic stirring speed is 200-500 rpm, and the stirring time is 1-12 h.

[0020] In step 4, the drying temperature is 40-60℃, and the drying time is 6-12 h.

[0021] The application is based on the application of modified transition metal sulfide thin film material in the preparation of fire warning sensor.

[0022] The fire warning sensor comprises a low-voltage power supply, a modified transition metal sulfide thin film material, and an alarm device, which are connected in series by wires.

[0023] The low-voltage power supply has a voltage of 5-25V, preferably 10-20V.

[0024] The modified transition metal sulfide-based film material has a thickness of 50-100μm.

[0025] The beneficial effects of the present application are embodied in:

[0026] 1. The preparation method of the modified TMDs nanosheet has the advantages of low cost, strong controllability, and batch production.

[0027] 2. The preparation process of the film is simple and green, and does not involve the use of any harmful reagents.

[0028] 3. The film prepared by the present application has good mechanical flexibility and strength, and can support a weight of more than 3000 times its own weight.

[0029] 4. The film material has excellent flame retardancy, and has the functions of rapid fire response and recyclable early warning under fire conditions, and can be used as an ideal fire warning sensor material. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a scanning electron micrograph of the modified molybdenum disulfide nanosheet in Example 1.

[0031] Figure 2 It is the infrared spectrum and the thermal gravimetric graph of (a) and (b) of tannic acid, bulk molybdenum disulfide, modified molybdenum disulfide in Example 1.

[0032] Figure 3 It is a photo of the modified molybdenum disulfide nanosheet aqueous dispersion prepared in Example 1 after being stored for two months, showing excellent storage stability and the characteristics of mass production.

[0033] Figure 4 It is a mechanical flexibility display diagram of the composite film paper-1 prepared in Example 1.

[0034] Figure 5 It is a scanning electron micrograph of the side of the composite film paper-1 prepared in Example 1: (a) low magnification; (b) high magnification; showing a pearl nacre-like multi-level micro-nano structure.

[0035] Figure 6 It is a mechanical strength display of the composite film material prepared in Example 1, and 16mg of the film sample can support a weight of more than 3000 times its own weight.

[0036] Figure 7 It is a comparison diagram of the composite film paper-1 prepared in Example 1 before and after burning, showing excellent flame retardancy.

[0037] Figure 8 Scanning electron microscope images of (a) surface and (b) side of the composite film paper-1 prepared in Example 1 after combustion test.

[0038] Figure 9 Schematic diagram of the composition of the fire-retardant early warning sensor system and its fire cycle early warning mechanism.

[0039] Figure 10 The test process of the early warning performance of the composite film paper-1 prepared in Example 1 shows a sensitive fire early warning response (less than 3s) and the ability to cycle early warning.

[0040] Figure 11 The corresponding resistance change graph of the composite film paper-1 prepared in Example 1 under the condition of 10 times flame attack in the application example.

[0041] Figure 12 Real-time resistance changes of the composite films paper-4, paper-5 and paper-6 prepared in Examples 4, 5 and 6. DETAILED DESCRIPTION

[0042] The application will be further described in detail below by combining the drawings and examples, the purpose of which is to more specifically and clearly set forth the content of the application rather than limit the protection scope of the application. Example 1:

[0043] 1. Mix 10 g of tannic acid powder and 20 g of molybdenum disulfide (size 30 μm) powder, place in a 300 ml ball mill tank, and perform ball milling treatment, ball milling speed 500 rpm, ball milling time 6 h.

[0044] 2. Disperse the above mixed powder in deionized water for ultrasonic treatment. The mass ratio of mixed powder to deionized water is 1:20; the ultrasonic power is 200 KW, the ultrasonic time is 20 min; then centrifugal washing for 3 times, centrifugal speed is 8000 rpm; centrifugal time is 10 min.

[0045] 3. Mix 20 mL of the above modified molybdenum disulfide water dispersion with a concentration of 10 mg / mL and 20 mL of cellulose nanofiber water dispersion with a concentration of 10 mg / mL (diameter 50 nm, length 15 μm), magnetically stir at room temperature for 12 h, speed 500 rpm.

[0046] 4. Next, transfer the uniform mixed solution to a mold, place it in a forced air oven for drying, temperature 45℃, dry for 12 h to obtain the composite film paper-1.

[0047] Figure 1SEM image of modified molybdenum disulfide nanosheets in Example 1, showing oligolayer structure, size around 500 nm.

[0048] Figure 2 (a) Infrared spectrum and (b) Thermogravimetric curve of tannic acid, bulk molybdenum disulfide, modified molybdenum disulfide in Example 1, the results show that tannic acid successfully modified molybdenum disulfide nanosheets.

[0049] Figure 3 The photo of modified molybdenum disulfide nanosheets aqueous dispersion prepared in Example 1 after storage for two months, showing excellent storage stability, showing the characteristics of mass production.

[0050] Figure 4 The mechanical display of composite film paper-1, showing excellent mechanical flexibility.

[0051] Figure 5 The scanning electron microscope image of the side of the composite film paper-1 prepared in Example 1, showing a pearl nacre-like multi-level micro-nano structure.

[0052] Figure 6 The mechanical strength display of the composite film material prepared in Example 1, 16 mg of film sample can support more than 3000 times its own weight, showing excellent mechanical strength.

[0053] Figure 7 The comparison of the composite film paper-1 prepared in Example 1 before and after burning, still maintaining the integrity of the structure after the flame continues to attack for 90 s, showing excellent flame retardancy.

[0054] Figure 8 The SEM images of the surface and side of the composite film paper-1 prepared in Example 1 after flame attack, it can be seen that the complete and dense surface structure can be porous side structure.

[0055] Figure 10 The test process of the early warning performance of the composite film paper-1 prepared in Example 1, showing sensitive fire warning response (less than 3 s) and recyclable warning ability. Example 2:

[0056] 1. Mix 10 g of tannic acid powder and 30 g of molybdenum disulfide (size 10 μm) powder, put it in a 300 ml ball mill tank, and carry out ball milling treatment, ball milling speed 200 rpm, ball milling time 2 h.

[0057] 2. Disperse the above-mentioned mixed powder in deionized water and perform ultrasonic treatment. The mass ratio of the mixed powder to deionized water is 1:100; the ultrasonic power is 50 KW and the ultrasonic time is 60 min; then centrifuge and wash 5 times, with a centrifugation speed of 3000 rpm and a centrifugation time of 5 min.

[0058] 3. Mix 10 mL of the modified molybdenum disulfide aqueous dispersion with a concentration of 10 mg / mL and 20 mL of cellulose nanofiber aqueous dispersion with a concentration of 10 mg / mL (diameter 200 nm, length 5 μm), and stir magnetically for 1 h at room temperature at a speed of 200 rpm.

[0059] 4. Next, the uniformly mixed solution is transferred to a mold and placed in a forced-air drying oven at 60℃ for 6 hours to obtain the composite film paper-2. Example 3:

[0060] 1. Mix 10g of sodium alginate powder and 20g of molybdenum disulfide powder (20 μm in size), place them in a 300ml ball mill jar, and ball mill them at 300rpm for 4 hours.

[0061] 2. Disperse the above mixed powder in deionized water and perform ultrasonic treatment. The mass ratio of mixed powder to deionized water is 1:50; the ultrasonic power is 100 KW and the ultrasonic time is 30 min; then centrifuge and wash twice, with a centrifugation speed of 6000 rpm and a centrifugation time of 20 min.

[0062] 3. Mix 15 mL of the modified molybdenum disulfide aqueous dispersion with a concentration of 10 mg / mL and 20 mL of cellulose nanofiber aqueous dispersion with a concentration of 10 mg / mL (diameter 150 nm, length 10 μm), and stir magnetically for 6 h at room temperature at a speed of 300 rpm.

[0063] 4. Next, the uniformly mixed solution is transferred to a mold and placed in a forced-air drying oven at 50℃ for 8 hours to obtain the composite film paper-3. Example 4:

[0064] 1. Mix 15g of tannic acid powder and 20g of tungsten disulfide powder (20 μm in size), place them in a 300ml ball mill jar, and ball mill them at 200rpm for 6 hours.

[0065] 2. The mixed powders were dispersed in deionized water and treated by ultrasonic. The mass ratio of mixed powders and deionized water was 1:20; the ultrasonic power was 150 KW, and the ultrasonic time was 15 min; then the solution was washed by centrifugation for 4 times, the centrifugal speed was 5000 rpm, and the centrifugal time was 40 min.

[0066] 3. 10 mL of the modified tungsten disulfide aqueous dispersion solution (10 mg / mL) and 20 mL of the cellulose nanofiber aqueous dispersion solution (10 mg / mL, diameter 50 nm, length 15 μm) were mixed, and then the mixture was stirred at room temperature for 8 h at a speed of 500 rpm.

[0067] 4. The uniform mixed solution was then transferred into a mold and dried in a blast oven at a temperature of 40°C for 12 h to obtain a composite film paper-4. Example 5

[0068] 1. 15 g of cellulose microcrystal powder and 20 g of tungsten diselenide powder (size 20 μm) were mixed and placed in a 300 ml ball mill tank for ball milling treatment, the ball milling speed was 200 rpm, and the ball milling time was 6 h.

[0069] 2. The mixed powders were dispersed in deionized water and treated by ultrasonic. The mass ratio of mixed powders and deionized water was 1:50; the ultrasonic power was 100 KW, and the ultrasonic time was 15 min; then the solution was washed by centrifugation for 4 times, the centrifugal speed was 4000 rpm, and the centrifugal time was 30 min.

[0070] 3. 20 mL of the modified tungsten diselenide aqueous dispersion solution (10 mg / mL) and 20 mL of the cellulose nanofiber aqueous dispersion solution (10 mg / mL, diameter 100 nm, length 15 μm) were mixed, and then the mixture was stirred at room temperature for 6 h at a speed of 300 rpm.

[0071] 4. The uniform mixed solution was then transferred into a mold and dried in a blast oven at a temperature of 45°C for 10 h to obtain a composite film paper-5. Example 6

[0072] 1. 10 g of tannic acid powder and 20 g of molybdenum diselenide powder (size 30 μm) were mixed and placed in a 300 ml ball mill tank for ball milling treatment, the ball milling speed was 500 rpm, and the ball milling time was 6 h.

[0073] 2. The mixed powders were dispersed in deionized water and treated by ultrasonic. The mass ratio of mixed powders and deionized water was 1:20; the ultrasonic power was 150 KW, and the ultrasonic time was 30 min; then the solution was washed by centrifugation for 5 times, the centrifugal speed was 6000 rpm, and the centrifugal time was 20 min.

[0074] 3. 10 mL of the above-mentioned modified molybdenum diselenide aqueous dispersion solution with a concentration of 10 mg / mL and 20 mL of cellulose nanofiber aqueous dispersion solution with a concentration of 10 mg / mL (diameter 50 nm, length 10 μm) were mixed, and the mixture was stirred at room temperature by magnetic stirring at a speed of 500 rpm for 4 h.

[0075] 4. Next, the uniform mixed solution was transferred to a mold and dried in a blast oven at a temperature of 45°C for 10 h to obtain a composite film paper-6. Example 7:

[0076] 1. 10 g of sodium alginate powder and 20 g of molybdenum diselenide powder (size 20 μm) were mixed and placed in a 300 ml ball mill tank for ball milling treatment at a speed of 300 rpm for 4 h.

[0077] 2. The mixed powders were dispersed in deionized water and treated by ultrasonic. The mass ratio of mixed powders and deionized water was 1:100; the ultrasonic power was 50 KW, and the ultrasonic time was 60 min; then the solution was washed by centrifugation for 5 times, the centrifugal speed was 8000 rpm, and the centrifugal time was 10 min.

[0078] 3. 15 mL of the above-mentioned modified molybdenum diselenide aqueous dispersion solution with a concentration of 10 mg / mL and 20 mL of cellulose nanofiber aqueous dispersion solution with a concentration of 10 mg / mL (diameter 100 nm, length 15 μm) were mixed, and the mixture was stirred at room temperature by magnetic stirring at a speed of 300 rpm for 6 h.

[0079] 4. Next, the uniform mixed solution was transferred to a mold and dried in a blast oven at a temperature of 50°C for 8 h to obtain a composite film paper-7. Example 8:

[0080] 1. 20 g of cellulose microcrystal powder and 20 g of tungsten disulfide powder (size 20 μm) were mixed and placed in a 300 ml ball mill tank for ball milling treatment at a speed of 500 rpm for 2 h.

[0081] 2. The mixed powders were dispersed in deionized water and treated by ultrasonic. The mass ratio of mixed powders and deionized water was 1:50; the ultrasonic power was 100 KW, and the ultrasonic time was 20 min; then the solution was washed by centrifugation for 3 times, the centrifugal speed was 6000 rpm, and the centrifugal time was 10 min.

[0082] 3. 10 mL of the modified tungsten disulfide aqueous dispersion solution (10 mg / mL) and 20 mL of the cellulose nanofiber aqueous dispersion solution (10 mg / mL) were mixed (diameter 80 nm, length 10 μm), and then the mixture was stirred at room temperature for 4 h at a speed of 500 rpm.

[0083] 4. The uniform mixed solution was then transferred into a mold and dried in a blast oven at a temperature of 60°C for 10 h to obtain a composite film paper-8. Example 9:

[0084] 1. 20 g of tannic acid powder and 20 g of tungsten diselenide powder (size 15 μm) were mixed and placed in a 300 ml ball mill tank for ball milling treatment, the ball milling speed was 300 rpm, and the ball milling time was 2 h.

[0085] 2. The mixed powders were dispersed in deionized water and treated by ultrasonic. The mass ratio of mixed powders and deionized water was 1:30; the ultrasonic power was 150 KW, and the ultrasonic time was 20 min; then the solution was washed by centrifugation for 4 times, the centrifugal speed was 5000 rpm, and the centrifugal time was 20 min.

[0086] 3. 15 mL of the modified tungsten diselenide aqueous dispersion solution (10 mg / mL) and 20 mL of the cellulose nanofiber aqueous dispersion solution (10 mg / mL) were mixed (diameter 80 nm, length 10 μm), and then the mixture was stirred at room temperature for 6 h at a speed of 400 rpm.

[0087] 4. The uniform mixed solution was then transferred into a mold and dried in a blast oven at a temperature of 55°C for 12 h to obtain a composite film paper-9. Example 10:

[0088] 1. 20 g of sodium alginate powder and 20 g of molybdenum diselenide powder (size 10 μm) were mixed and placed in a 300 ml ball mill tank for ball milling treatment, the ball milling speed was 500 rpm, and the ball milling time was 4 h.

[0089] 2. The mixed powder is dispersed in deionized water and ultrasonic treated. The mass ratio of mixed powder and deionized water is 1:50; the ultrasonic power is 100 KW, and the ultrasonic time is 20 min; then centrifugal washing is performed once, with a centrifugal speed of 8000 rpm and a centrifugal time of 10 min.

[0090] 3. 10 mL of the above-mentioned modified molybdenum diselenide aqueous dispersion solution with a concentration of 10 mg / mL and 20 mL of cellulose nanofiber aqueous dispersion solution with a concentration of 10 mg / mL (diameter 100 nm, length 15 μm) are mixed, and magnetic stirring is performed at room temperature for 4 h at a speed of 500 rpm.

[0091] 4. Next, the uniformly mixed solution is transferred to a mold and dried in a blast oven at a temperature of 45°C for 12 h to obtain a composite film paper-10.

[0092] Application Example 1

[0093] To demonstrate that the composite film material prepared in the application has a sensitive fire response and a recyclable early warning function, the composite film paper-1 prepared in Example 1 is subjected to fire early warning testing. A low-voltage power supply, a resistance machine, an alarm lamp and paper-1 are connected with wires to form a series circuit. As shown in Figure 10 , the circuit is not conductive at the beginning, and the alarm lamp is off; after 3 s of flame attack, the alarm lamp is triggered; after the flame is removed, the alarm signal disappears immediately; when the flame attacks again, the circuit is conductive again, and the alarm lamp lights up again. In addition, the applicant also uses a resistance machine to monitor the resistance change of paper-1 under the condition of ten times of flame attack. As shown in Figure 11 , it can be seen that the resistance value of paper-1 decreases rapidly after the flame attack, and the resistance value changes with the flame attack and removal, and the conversion between the conductor and the insulator, thereby realizing the function of recyclable fire early warning. Figure 12 The real-time resistance change of the composite films paper-4, paper-5 and paper-6 prepared in Examples 4, 5 and 6 also demonstrates the sensitive fire early warning response and the recyclable early warning capability.

Claims

1. A method for preparing thin film materials based on modified transition metal sulfides, characterized in that... Includes the following steps: Step 1: Using hydroxyl-containing biomass molecules as modifiers, modified and exfoliated block TMDs are obtained through ball milling process; Step 2: Disperse the modified TMDs powder obtained in Step 1 in deionized water, further peel off the TMDs under ultrasonic conditions in a water bath, and obtain a stable modified TMDs nanosheet aqueous dispersion after centrifugation and washing. Step 3: Mix the modified TMDs nanosheet aqueous dispersion and the cellulose nanofiber aqueous dispersion, and then stir magnetically to obtain a uniform mixed solution. Step 4: Transfer the obtained mixed solution into a mold and dry it in a forced-air oven to obtain a composite film; In step 1, the hydroxyl-containing biomass molecule is one or more of tannic acid, sodium alginate, and cellulose microcrystals; In step 1, the TMDs are one or more of molybdenum disulfide, tungsten disulfide, molybdenum diselenide, and tungsten diselenide, and the size of the bulk TMDs is in the range of 10-30 μm. In step 3, the diameter of the cellulose nanofibers is in the range of 50-200 nm and the length is in the range of 5-15 μm.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the hydroxyl-containing biomass molecule to the TMDs is 1:1 to 1:

3.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the cellulose nanofibers to the modified TMDs nanosheets is in the range of 1:1 to 1:

2.

4. The application of the thin film material based on modified transition metal sulfide prepared by any one of the preparation methods in claims 1-3 in the preparation of fire early warning sensors.

5. The application according to claim 4, characterized in that: The fire warning sensor includes a low-voltage power supply, a thin film material based on modified transition metal sulfides, and an alarm device, all connected by wires.

6. The application according to claim 5, characterized in that: The voltage of the low-voltage power supply is 5-25V.

7. The application according to claim 5, characterized in that: The thickness of the thin film material based on modified transition metal sulfides is 50-100 μm.

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